Gut Immunity

Question 1

Damaging agents to GIT

Answer 1

▪️acid and pepsin 
▪️drugs-alcohol and aspirin 
▪️refluxed bile 
▪️smoking 
▪️microorganisms 
▪️ischemia-poor blood supply 
▪️food allergens

Question 2

Protective agents to GIT

Answer 2

▪️mucus-HCO3
▪️cell membranes 
▪️cell migration and renewal 
▪️immune system 
▪️programmed cell death 
▪️acid inhibition

Question 3

Mucus-HCO3 barrier

Answer 3

▪️in rich acid and pepsin environments in the GIT:
-mucus traps water
-HCO3 is secreted from epithelial cells in response to mucosal prostaglandins
-create pH diffusion gradient
-slows down acid that might be permeating through
-cells are at correct pH
▪️tight junctions in stomach are quite tight, if acid does leak through it is taken away by blood flow

Question 4

What happens when acid gets through the GIT

Answer 4

▪️acid breathing mucosal reaches nerves which sense acid levels
▪️signal sent to brain
▪️brain then stimulates arterioles to relax and increase blood flow to area-hyperaemia
-brings in oxygen and nutrients for cells to regenerate
▪️if acid reaches blood vessel, get spiting of blood in GIT

Question 5

Restitution of GIT

Answer 5

▪️rapid repair of GIT lining
▪️with in 30mins- replaces with thinner epithelium
▪️key players:
-gastrin-promotes cell growth and movement
-prostaglandins- increased blood flow
-growth factors
-regenerating protein (Reg)-organises epithelium so cells are in the right place

Question 6

Peyer’s patches

Answer 6

▪️senses what is happening in gut lumen
▪️islands of immune tissue-ileum and colon
▪️no villi-dome epithelium over-lining lymphoid follicle
-lack mucous barrier on top so can sample lumen for bacteria
▪️contain microfold cells(M cells)-move bacteria across the cells to immune cells (mast cells, dendritic cells, macrophages)
-T cells to release cytokines into blood for inflammatory response
-peristalsis may be enhance to clear away any pathogens
-enhance mucous production to protect cells
-AB production (IgA)

Question 7

Life and death of an enterocyte

Answer 7

▪️cells from crypt take 3-6 days to move up to villus
▪️damaged cells undergo apoptosis
▪️1400 cells/villus/day are shed
▪️tight junctions make sure no gaps are left when a cells sheds

Question 8

Vomiting reflex

Answer 8

▪️stimulus
-smell, taste, over-distension, pain
▪️signal sent to vomiting centre in medullary initiate reflex
▪️phrenic nerve to fixes diaphragm for inspiration to create intra-adominal pressure
▪️contract stomach wall
▪️contact pylorus to stop contents form entering SI
▪️LOS and UOS relax to allow pressure to force food up.